Fracture Strength of Implant Screw-Retained All-Ceramic Crowns with the Use of the Angulated Screw Channel: A Pilot Study

To correct for angulation discrepancies in the maxilla, implant companies have designed angulated screw channel (ASC) abutments. The design of these abutments allows for the restorative screw channel to be placed up to 25 degrees off the center axis of the implant. Minimal independent research has been published to evaluate the fatigue resistance of this implant-abutment connection. This study evaluated the fracture strength of a newly designed zirconia crown with a 25-degree angulated screw channel (n = 5) vs a straight channel (n = 5). Each specimen was subjected to an off-axis compression load from an MTS cyclic loading machine with a custom-designed indenter simulating a natural dentition. All the 25-degree angulated screw channel specimens failed, with four of the five (80%) catastrophically failing. Four of the five straightchannel specimens failed, with two of the five (40%) catastrophically failing. Results revealed the potential abutment fracture from internal stresses at the screw-zirconia and metallic-zirconia interfaces. Further research is needed to test the use of all-ceramic crowns with the use of the angulated screw channel.